Double-stranded structures in nuclear and cytoplasmic RNA of rat liver.

Double-stranded segments are found in poly(A)+hnRNA as well as in poly(A)-hnRNA, but in the second case they have partly intermolecular character and may originate from an interaction between primary transcripts and snRNA. Fragments of hnRNA containing double-stranded segments are preferentially removed from the nucleus. In cytoplasmic poly(A)+RNA double-stranded segments longer than 20 base pairs represent about 2%. In cytoplasmic poly(A)-RNA intermolecular double-stranded segments derived from rRNA prevail. Double-stranded fragments from nuclear RNP and free cytoplasmic mRNP exhibit similar affinity to hydroxyapatite but their base compositions are different: low content of adenine and high of guanosine in nuclear in contrast to nearly symmetrical base composition in cytoplasmic fragments.